High-voltage semiconductor component

ABSTRACT

A semiconductor component having a semiconductor body comprises a blocking pn junction, a source zone of a first conductivity type and bordering on a zone forming the blocking pn junction of a second conductivity type complementary to the first conductivity type, and a drain zone of the first conductivity type. The side of the zone of the second conductivity type faces the drain zone forming a first surface, and in the region between the first surface and a second surface areas of the first and second conductivity type are nested in one another. The areas of the first and second conductivity type are variably so doped that near the first surface doping atoms of the second conductivity type predominate, and near the second surface doping atoms of the first conductivity type predominate. Furthermore a plurality of floating zones of the first and second conductivity type is provided.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of copending U.S. patentapplication Ser. No. 09/786,022 filed Nov. 9, 2001.

TECHNICAL FIELD

[0002] The present invention concerns a semiconductor device with asemiconductor body having a blocking pn-junction, a first zone of afirst conductivity type, which is connected to a first electrode andabuts one of the zones of a second conductivity type opposite the firstconductivity type forming the blocking pnj unction, and with a secondzone of the first conductivity type, which is connected to a secondelectrode, whereby the side of the zone of the second conductivity typefacing the second zone forms a first surface and in the region betweenthe first surface and a second surface, which lies between the firstsurface and the second zone, areas of the first and of the secondconductivity type are nested.

BACKGROUND OF THE INVENTION

[0003] Such semiconductor devices are also known as compensationdevices. Such compensation devices are, for example, n- or p-channel MOSfield effect transistors, diodes, thyristors, GTOs, or other components.In the following, however, a field effect transistor (also referred tobriefly as “transistor”) is assumed as an example.

[0004] There have been various theoretical investigations spread over along period of time concerning compensation devices (cf. U.S. Pat. Nos.4,754,310 and 5,216,275) in which, however, specifically, improvementsof the on-resistance R_(DS)(on) but not of stability under current load,such as, in particular, robustness with regard to avalanche and shortcircuit in the high-current operation with high source-drain voltage,are sought.

[0005] Compensation devices are based on mutual compensation of thecharge of n- and p-doped areas in the drift region of the transistor.The areas are spatially arranged such that the line integral above thedoping along a line running vertical to the pn-junction in each caseremains below the material-specific breakdown voltage (silicon:approximately 2×10¹² cm⁻²). For example, in a vertical transistor, as iscustomary in power electronics, p-and n-columns or plates, etc. may bearranged in pairs. In a lateral structure, p- and n-conductive layersmay be stacked on each other laterally alternating between a groove witha p-conductive layer and a groove with an n-conductive layer (cf. U.S.Pat. No. 4,754,310).

[0006] By means of the extensive compensation of the p- and n-doping,the doping of the current-carrying region (for n-channel transistors,the n-region; for p-channel transistors, the p-region) can besignificantly increased, whereby, despite the loss in current-carryingarea, a clear gain in on-resistance R_(DS)(on) results. The blockingcapability of the transistor depends substantially on the differencebetween the two dopings. Since, because of the reduction of theon-resistance, a doping higher by at least one order of magnitude of thecurrent-carrying area is desirable, control of the blocking voltagerequires controlled adjustment of the compensation level, which can bedefined for values in the range ≦±10%. With a greater gain inon-resistance, the range mentioned becomes even smaller. Thecompensation level is then definable by

[0007] (p-doping−n-doping)/n-doping

[0008] or by

[0009] charge difference/charge of one doping area.

[0010] Other definitions are, however, possible.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a robustsemiconductor component of the kind initially mentioned, to be firstlydistinguished by a high “avalanche” ruggedness and high current loadcapacity before and/or during breakdown and secondly simple to producewith reproducible properties in view of technological latitudes offluctuation of manufacturing processes.

[0012] This object is accomplished according to the invention, in asemiconductor component of the kind initially mentioned, in that theregions of the first and second types of conductivity are so doped thatcharge carriers of the second conductivity type predominate in regionsnear the first surface and charge carriers of the first conductivitytype in regions near the second surface.

[0013] Preferably, the regions of the second conductivity type do notextend as far as up to the second zone, so that between said secondsurface and the second zone, a weakly doped region of the firstconductivity type remains. It is possible, however, to allow the widthof this region to go to “zero.” The weakly doped region, however,provides certain advantages, such as enhancement of the barrier voltage,“smooth” profile of the electrical field strength, or improvement ofcommutation properties of the inverse diode.

[0014] In another refinement of the invention, it is provided thatbetween the first and second surfaces, a degree of compensation effectedby the doping is so varied that atomic residues of the secondconductivity type dominate near the first surface and atomic residues ofthe first conductivity type near the second surface. In other words,there are sequences of p, p{overscore ( )}, n{overscore ( )}, n or n,n{overscore ( )}, p{overscore ( )}, p layers between the two surfaces.

[0015] Advantageous improvements of the semiconductor device accordingto the invention (hereinafter also referred to as “compensation device”)are disclosed by the other dependent claims.

[0016] The effect of the areas nested in each other, alternatingdifferent conductivity types, on the electrical field, is, in contrastto a conventional DMOS transistor, for example, as follows (“lateral”and “vertical” refer in the following to a vertical transistor):

[0017] (a) There is a cross-field, “lateral” to the direction of theconnection between the electrodes, the strength of which depends on theproportion of the lateral charge (line integral perpendicular to thelateral pn-junction) relative to the breakdown charge. This field leadsto the separation of electrons and holes and to a reduction in thecurrent-carrying cross-section along the current paths. This fact is ofprimary significance for the understanding of the processes inavalanche, of the breakdown characteristic curve, and of the saturationregion of the output characteristics diagram.

[0018] (b) The “vertical” electrical field parallel to the direction ofthe connection between the electrodes is determined locally by thedifference between the adjacent dopings. This means that with an excessof donors (n-loaded distribution: the charge in the n-conductive areasexceeds the charge of the p-areas) on the one hand, a DMOS-like fielddistribution (maximum of the field on the blocking pn junction,decreasing field in the direction of the opposing back of the device)appears, whereby the gradient of the field is, however, clearly lessthan would correspond to the doping of the n-area alone. On the otherhand, however, by overcompensation of the n-conductive area withacceptors, a field distribution rising in the direction of the back ispossible (p-loaded distribution: excess of acceptors compared to thedonors). In such a design, the field maximum lies at the bottom of thep-area. If the two dopings are exactly compensated, there is ahorizontal field distribution.

[0019] With an exact horizontal field distribution, the maximum of thebreakdown voltage is obtained. If the acceptors or the donorspredominate, the breakdown voltage drops in each case. If the breakdownvoltage is then plotted as a function of the degree of compensation, aparabolic characteristic is obtained.

[0020] Constant doping in the p- and n-conductive areas or even alocally varying doping with periodic maxima of equal height results in acomparatively sharply pronounced maximum of the “compensation parabola”.For the benefit of a “production window” (including the fluctuations ofall relevant individual processes), a comparatively high breakdownvoltage must be steered for in order to obtain reliable yields andproduction reliability. Consequently, the objective must be to make thecompensation parabola as flat and as broad as possible.

[0021] When the blocking voltage is applied to the device, the driftregion, i.e., the region of the areas of opposite doping arranged inpairs, is cleared of mobile charge carriers. The positively chargeddonor cores and the negatively charged acceptor cores remain in thespreading space charge region. They then determine the course of thefield.

[0022] The flow of current through the space charge region causes achange in the electric field when the concentration of the chargecarrier associated with the flow of current comes into the region of thebackground doping. Electrons compensate donors; holes compensateacceptors. For the stability of the device, it is also very importantwhich doping predominates locally, where charge carriers are generated,and how their concentrations result along their current paths.

[0023] For the following embodiments, for an understanding of the basicmechanism, initially a constant doping of the p- and n-conductive areasis assumed.

[0024] In the on-state and especially in the saturation region of theoutput characteristics of a MOS transistor, a pure stream of electronsflows from the channel into an n-doped area, also referred to as a“column” in a vertical transistor, whereby in the base an increasingfocusing of the flow of current occurs because of the electricalcross-field. High-current stability is promoted by dominance of then-doping; however, since the channel region with its positivetemperature coefficient eliminates inhomogeneous current distribution ina cell field, this mode of operation is rather uncritical. Reduction inthe current density is obtained through partial shadowing of the channelconnection (cf. DE 198 08 348 A1).

[0025] With regard to the breakdown characteristic or its course, thefollowing must be taken into consideration: The generation of electronsand holes occurs in the region of maximum field strength. The separationof the two types of charge carriers is performed by the electricalcross-field. Along the two current paths in the p- and n-area,respectively, focusing and further multiplication occurs. Ultimately,also no effect of a partial channel shadowing occurs. Stability ispresent only when the mobile charge carriers cause a rise in theelectrical field outside their source and thus a rise in the breakdownvoltage of the respective cell. For compensation devices this meansstability in the p- and n-loaded region, but not in the maximum of thecompensation parabola. In the p-loaded region, the breakdown occurs atthe “bottom” of the column. The electrons flow out of the drift regionand thus do not affect the field. The holes are pulled through thelongitudinal electrical field to the top source contact. In the process,the hole current is focused along its path by the electricalcross-field: The current density rises here. Thus, the longitudinalelectrical field is initially affected near the surface. As a result ofcompensation of the excess acceptor cores (p-loaded distribution), areduction in the gradient of the electrical field and a rise in thebreakdown voltage occur. This situation is stable as long as the fieldthere remains clearly below the critical field strength (for silicon:approximately 270 kV/cm for a charge carrier concentration ofapproximately 10¹⁵ cm⁻³).

[0026] In the n-loaded region with an excess of donors, the breakdown isnear the surface. The holes flow to the source contact and still affectthe field on their path from their source to the p-well. The objectivemust consequently be to place the breakdown location as near as possibleto the p-well. This can be accomplished, for example, by a localelevation in the n-doping. The electrons flow through the complete driftzone to the back and likewise affect the field along their current path.Stability is obtained when the effect of the electron current prevailsover that of the hole current. Since the geometry of the cellarrangement plays an important role here, there is a region of stableand instable characteristic curves especially near the maximum ofcompensation parabola.

[0027] The conditions in the avalanche are very similar to those of abreakdown. The currents are, however, clearly higher and have with arated current as much as twice the rated current of the transistor.Since the electrical cross-field always causes a clear focusing of thecurrent, in compensation devices the stability range is left atcomparatively low current loads. Physically, this means that thecurrent-induced rise in the field has already advanced so much thatlocally the breakdown field strength has been reached. The longitudinalelectrical field can then not rise further locally; the curvature of thelongitudinal electrical field, however, increases which results in adrop in the breakdown voltage of the cell in question. In thecharacteristic curve of an individual cell and also in the simulation,this is reflected by a negative differential resistance; i.e., thevoltage drops as the current rises. In a large transistor with more than10,000 cells this results in a very rapid inhomogeneous redistributionof the current. A filament is formed, and the transistor melts locally.

[0028] This yields the following consequences for the stability ofcompensation devices:

[0029] (a) Due to the separation of electrons and holes there is no“auto-stabilization” as with IGBTs and diodes. Instead, the degree ofcompensation, field distribution, and breakdown location must be setexactly.

[0030] (b) On the compensation parabola, with constant doping of the p-and n-areas or “columns”, there are stable regions in the clearly p- andin the clearly n-charged regions. The two regions are not contiguous.Thus, there is only an extremely small production window. With constantdoping of the p- and n-areas or columns, the compensation parabola isextremely steep. The breakdown location moves within a few percent fromthe bottom of the p-column in the direction of the surface.

[0031] (c) For each compensation device, there is a current destructionthreshold in the avalanche which is directly coupled with the degree ofcompensation. The degree of compensation, on the other hand, determinesthe achievable breakdown voltage and effects the R_(DS)(on) gain.

[0032] (d) With constant doping of the p- and n-areas, the devicesare—as mentioned above—instable near the maximum of the compensationparabola. This results in the fact that the devices with the highestblocking voltage are destroyed in the avalanche test.

[0033] As explained above, to prevent the disadvantages, the degree ofcompensation is varied along the doping areas, i.e., in a verticalstructure from the top in the direction of the back of the transistor,such that the atomic cores of the second conductivity type dominate nearthe surface and the atomic cores of the first conductivity type dominatenear the back.

[0034] The resultant field distribution has a “hump-shaped” curve with amaximum at approximately one-half of the depth (cf. FIG. 6). Thus, boththe electrons and holes affect the field distribution in the breakdownand in the avalanche. Both types of charge carriers have a stabilizingeffect, since in each case they run from their source into areas inwhich they compensate the dominating excess background doping. There isthus a continuous stability range from p-loaded to n-loaded degrees ofcompensation.

[0035] A variation of the degree of compensation due to productionfluctuations shifts the breakdown location only slightly in the verticaldirection and continuously back and forth, as long as this variation isless than the technically adjusted variation of the degree ofcompensation. The size of this modification of the degree ofcompensation also determines the limits of the stability range. Thus,the production window becomes freely selectable.

[0036] The focusing of the currents is clearly less pronounced sinceboth types of charge carriers travel only one-half the path in theregion of the compressing electrical cross-field. Thus, the devices canbe stressed with clearly higher currents in the avalanche.

[0037] Since in a variation of the degree of compensation, e.g., in thedirection toward “n-loading”, the electrical field increases in eachcase in the upper area of the drift region, but simultaneously decreasesin the lower area (vice versa with variations toward p-loadeddistribution), the breakdown voltage varies only relatively little as afunction of the degree of compensation. Thus, the compensation parabolabecomes preferably flat and wide.

[0038] The vertical variation of the degree of compensation can beeffected by variation of the doping in the p-region or by variation ofthe doping in the n-region or by variation of the doping in bothregions. The variation of the doping along the column may have aconstant rise or be in a plurality of steps. In principle, the variationincreases monotonically from a p-loaded degree of compensation to ann-loaded degree of compensation.

[0039] The invention can be readily applied even with p-channeltransistors. In that case, an appropriately altered course of thesemiconductor regions occurs: A (p, p-dominated, n-dominated, n) courseis replaced by an (n, n-dominated, p-dominated, p) course.

[0040] The stability limits are reached on the n-loaded side when thefield runs horizontally near the surface over an appreciable part of thedrift region. On the p-loaded side the stability limits are reached whenthe field runs horizontally near the bottom of the compensating columnregion over a noticeable part of the drift region.

[0041] In general, the compensation parabola becomes flatter and widerthe greater the gradient of the degree of compensation. The breakdownvoltage in the maximum of the compensation parabola drops accordingly.

[0042] Another important limitation of the variation of the degree ofcompensation results from the requirement to remain below the breakdowncharge. In addition, with greater elevation of the p-column doping nearthe surface, current pinch-off effects occur near the surface (lateralJFET effect).

[0043] For 600 V devices, a variation of the degree of compensationlengthwise of the p- and n-areas of 50%, for example, is advantageous.

[0044] Although above the starting point has been primarily a verticaltransistor, the semiconductor device according to the invention can, inprinciple, have a vertical or even a lateral structure. With a lateralstructure, n- and p-conductive plate-shaped areas are, for example,arranged laterally stacked in each other.

[0045] Applications for such lateral transistors are, for example, foundin the smart power sector or in microelectronics; vertical transistorsare, in contrast, produced primarily in power electronics.

[0046] The vertical modification of the degree of compensation is verysimple to implement since in the individual epitaxial planes, only theimplantation dose must be altered. The “real” compensation dose is thenimplanted in the middle epitaxial layer; below that, for example, 10%less in each case, above that, for example, 10% more in each case.However, instead of the implantation dose, it is possible to alter theepitaxial doping.

[0047] By means of the more manageable variation, it is possible toreduce the production costs. The number of necessary epitaxial layerscan be reduced, and the openings for the compensation implantation canbe reduced as a result of greater variation of the implanted dose due tothe greater relative variation of the resist dimension withsimultaneously prolonged subsequent diffusion for the merging of theindividual p-regions into the “column”.

[0048] The structure according to the invention is produced by thefollowing individual steps:

[0049] First, a multi-μm-thick, n-doped epitaxial layer is applied to asemiconductor substrate. The p-doping ions are introduced into thisepitaxial layer via a resist mask by means of ion implantation. Next,the entire process is repeated as often as necessary until there is anadequately thick n-multi epitaxial layer with embedded p-centers alignedwith each other and stacked. The production of the actual device thenoccurs, by means of, for example, the processing of the base zones, thesource zones, the front metalization, and the gate electrodes in a fieldeffect transistor. By thermal diffusion, the p-doped centers merge intoa rippled vertical column. Due to intrinsic compensation, theconcentration of the p- or n-doping material is always substantiallyhigher than the resultant electrically active doping.

[0050] The ripple of the vertical column is expressed in a varyingacceptor-donor ratio k_(e)(z) per horizontal plane. The electricalcompensation varies accordingly in each horizontal plane in thesemiconductor body. The ripple of the column causes no significantchange in the horizontal field. Consequently, in the firstapproximation, the contribution U_(Bh) is considered unaffected by theripple.

[0051] In the vertical direction, layers with non-horizontallycompensated p-and n-charges alternate. An epitaxial layer corresponds toa complete ripple period and, consequently, corresponds to two adjacentpn-junctions. Due to the production fluctuations in the epitaxy cycles,the charge balance is not equalized over the entire volume of apn-junction such that the degree of compensation does not equal 0.

[0052] In a semiconductor device according to the present invention, thevoltage consumed in the blocked state in the cell field between anodesand cathodes or in a field effect transistor vertically between sourceand drain must also be discharged laterally on the edge of thesemiconductor device. Semiconductor devices are often operated up to abreakdown. In this case, a very high current flows through the impactionization which occurs. In order not to destroy the semiconductordevice, no excessively high current densities may occur, i.e., thebreakdown current must be distributed as uniformly as possible over theentire semiconductor device. However, this requirement can be fulfilledonly if the cell field carries the majority of this current. If thesemiconductor device breaks down in the edge structure at a smallerblocking voltage than the cell field, this results in most cases inirreversible thermal damage to the semiconductor device. Thesemiconductor device must, consequently, be avalanche-rugged.Avalanche-rugged semiconductor devices, especially vertical transistors,reduce the safety distance necessary to manage overvoltages, whereby inmany applications comparatively low-blocking transistors may be used,which require at the same R_(DS)(on) a comparatively small semiconductordevice surface and are thus more economical. With conventionalhigh-voltage MOSFETs, this is very significant since the R_(DS)(on) ofthese transistors rises disproportionately with the breakdown voltage.With conventional power devices, expensive surface-mounted structures orstructures near the surface usually result in the situation that thesemiconductors device edge can block more voltage than the cell field.The lower-lying semiconductor device volume is homogeneously doped solow that it withstands the necessary voltage without structuring. Withthe semiconductor devices according to the present invention, which usethe production process of intrinsic compensation, the demands withregard to the edge structure are intensified because here even thelower-lying volumes under the edge must be processed. The materialactually accommodating the blocking voltage, i.e., the epitaxial layerabove the highly doped semiconductor substrate, is relatively low ohmicand will only block a fraction of the required voltage. The blockingcapability for the cell field is achieved only with the introduction ofthe counter doped columns.

[0053] For the volume below the edge, there are, in principle, twodifferent processing methods:

[0054] 1. The semiconductor edge may be processed separately from thecell field, i.e., in additional steps. An overall counter doping of thesubstrate on the semiconductor edge, e.g., by means of overall edgeimplantation and diffusion, is conceivable. Thus, an overallintrinsically compensated and thus highly blocking edge can be produced.Such a procedure is, however, associated with very high costs.

[0055] 2. The column structure in the cell field is continued into theedge, whereby the substrate is also built up to basically the sameblocking voltages as in the cell field. A minimal increase, for example,in the dielectric strength of the edge may be obtained in many cases bymeans of a suitable variation of the deep compensation profile of thecolumns, as this has been described on the preceding pages for the cellfield, whereby, however, the tolerance range compared to the cell fieldand thus the tolerance range of the entire semiconductor device becomessmaller. Additionally, additional effects may provoke breakdown on theedge of the semiconductor device.

[0056] On the one hand, the surface-mounted edge structures orstructures near the surface cause additional field distortions andgenerate centers of high field strength.

[0057] On the other hand, it may be necessary to apply an expedientnegative “error charge” to the edge, which causes a curvature of theequipotential lines toward the semiconductor device surface, wherebythese can be picked up and carried by the surface structure. Thiscorresponds to a field discharge on the semiconductor device edge. Thiserror charge condition may also cause a voltage-induced prematurebreakdown of the semiconductor device edge compared to the cell field.

[0058] Accordingly, it is best to reduce the horizontal components ofelectric field and simultaneously the vertical ripple of thecompensation profile on the edge. Both result in higher blockingvoltages on the semiconductor device edge. To implement this, the localseparation must be eliminated or at least weakened in the charge centersof opposing polarity, i.e., an intrinsic compensation must beundertaken.

[0059] Thus, a high-voltage resistant edge structure is created, whichconsists of a plurality of floating zones of the second conductivitytype, which are separated by intermediate zones of the firstconductivity type, whereby the width of the intermediate zones and widthof the floating zones are smaller than the width of the areas of thefirst and of the second conductivity type, which are nested in eachother inside the cell fields. These floating zones and intermediatezones are doped such that the charge carriers of floating zones and ofintermediate zones are completely cleared with the application ofblocking voltage.

[0060] Thus, preferably, the edge volume is processed in one and thesame operation, whereby both the thickness of an individual epitaxiallayer and the cell grid is reduced in size in the edge region, yieldingat the end of the process homogeneous dopant distribution for both typesof charge carriers for each edge cell. With regard to the ratio ofunmasked surface per cell to the total cell surface in the edge region,the charge applied by implantation can be ideally adapted to the chargewhich is defined by the epitaxy. In order to achieve ideal blockability,a charge balance, i.e., intrinsically compensated condition, is sought.

[0061] Preferably, the thickness of the individual epitaxial layers willbe designed according to specifications which the cell field defines.This again yields a vertically rippled compensation profile on thesemiconductor edge, but in a substantially weaker form than in the cellfield. A reduction in the cell grid results in the fact that theresolution of the doping material source is reduced, whereby theboundaries of the individual diffusion fronts become blurred.

[0062] An additional advantage of the edge design described is thecoupling between the production defects in the edge and in the cellfield since error mechanisms act in both regions in the same direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The invention is explained in detail in the following withreference to the drawings. They depict:

[0064]FIG. 1 a top view of an n-channel lateral MOS transistor accordingto a first exemplary embodiment of the invention,

[0065]FIG. 2 a cross-section of an n-channel lateral MOS transistor withV-shaped grooves according to a second exemplary embodiment of theinvention,

[0066]FIG. 3a through 3 d various layouts in the semiconductor deviceaccording to the invention,

[0067]FIG. 4 a cross-section through an n-channel lateral MOS transistoraccording to a third exemplary embodiment of the invention,

[0068]FIG. 5 the course of the degree of compensation K along the lineC-D in FIG. 4,

[0069]FIG. 6 the course of the electrical field along the line C-D inFIG. 4,

[0070]FIG. 7 the course of the breakdown voltage as a function of thedegree of compensation for constant doping and for variable doping,

[0071]FIG. 8 a concrete example of the cell design for an n-channel MOStransistor,

[0072]FIGS. 9a through 9 c various square edge structure layouts in thesemiconductor device according to the invention,

[0073]FIGS. 10a through 10 c various strip edge structure layouts in thesemiconductor device according to the invention,

[0074]FIG. 11a hexagonal edge structure layout in the semiconductordevice according to the invention,

[0075]FIG. 12a cross-section through an n-channel MOS transistoraccording to a fourth exemplary embodiment with an edge structurelayout, and

[0076]FIG. 13a cross-section through an n-channel MOS transistoraccording to a fifth exemplary embodiment with a different edgestructure layout.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0077]FIG. 1 depicts a top view of an n-channel MOS transistor with ann⁺-conductive drain zone 15, an n⁺-conductive source zone 16, a gateelectrode 8, and a p-conductive area 5. This p-conductive area 5 extendsfinger-like into an n-conductive area 4 on a semiconductor substrate 1,such that the areas 4 and 5 are “nested” in each other. The gateelectrode 8 may, for example, be made of polycrystalline silicon,whereas an isolation layer not shown in FIG. 1 below this gate electrode8 is made, for example, of silicon dioxide and/or silicon nitride. Inthe p-conductive area 5, a p-charge excess is present in a zone I; a“neutral” charge, in a zone II; an n-charge excess, in a zone III. Thismeans that in the area 5 in the zone I, the p-charge dominates thecharge of the surrounding n-conductive area 5; that also in the zone II,the p-charge exactly compensates the charge of the surroundingn-conductive area 5; and that in the zone III, the p-charge is less thanthe charge of the surrounding n-conductive area 5. It is thussignificant that the charge of the p-area 5 is variable whereas thecharge of the n-areas 4 is in each case constant.

[0078] The p-conductive area 5 extends from the edge of the source zone16, i.e. from a surface A to a dashed line surface B in the n-conductiveregion 4. This surface B is positioned at a distance from the drain zone15, such that there is, between the surface B and the drain zone 15, ann-conductive region 13 in which there is no “nesting” with p-conductiveregions 5. However, it is also possible to shift the surface B to theedge of the drain zone 15, such that there is no n-conductive region 13.Advantageously, however, the surface B is positioned at a distance fromthe drain electrode 15, which results in an increase of the blockingvoltage, a smoother course of the electrical field, and an improvementof the commutating characteristics of the inverse diode.

[0079]FIG. 2 depicts a cross-section through another exemplaryembodiment of the semiconductor device according to the invention in theform of an n-channel MOS transistor with a drain electrode 2 and a gateinsulation layer 9 between the gate electrode 8 and the channel region,which is provided under the insulation layer 9 between a source zone 16and a drain zone 15 in a p-conductive region 5. Also, in this exemplaryembodiment, the p-conductive areas 5 in the zones I, II, and III havevariable doping, as was explained above with reference to FIG. 1.

[0080] The exemplary embodiments of FIGS. 1 and 2 depict two preferreddesign possibilities for lateral structures of the semiconductor deviceaccording to the invention. Essential in the two structures is the factthat the reported variable doping is present in the areas 5 and thatthese areas 5 do not reach the drain zone 15, i.e., terminate in asurface B at a distance from this drain zone 15. However, it is possibleto move the surface B toward the edge of the drain zone 15. As statedabove, the degree of compensation can be obtained by variation of thedoping of the p-conductive areas 5 or of the n-conductive areas 4.

[0081]FIGS. 3a through 3 d depict various layouts for the semiconductordevice according to the invention with hexagonal polysilicon structures17 and polysilicon openings 18 (FIG. 3a), in which aluminum contactholes 19 (FIG. 3b) may be provided. FIG. 3c depicts a layout withrectangular polysilicon structures 20 and corresponding polysiliconopenings 18 and aluminum contact holes 19, whereas FIG. 3d schematicallydepicts, in a top view and in cross-section, a strip structure withpolysilicon gate electrodes 8 and aluminum electrodes 21.

[0082]FIGS. 3a through 3 d depict how the semiconductor device accordingto the invention can be designed with different structures.

[0083]FIG. 4 depicts a cross-section through an n-channel MOS transistorwith an n⁺-conductive silicon semiconductor substrate 1, a drainelectrode 2, a first n-conductive layer 13, the second layer 3 withn-conductive areas 4 and p-conductive areas 5, p-conductive zones 6,n-conductive zones 7, gate electrodes 8 made, for example, frompolycrystalline silicon or metal, which are embedded in an isolatinglayer 9 made, for example, from silicon dioxide, and a sourcemetalization 10 made, for example, from aluminum. Here again, thep-conductive areas 5 do not reach the n⁺-conductive semiconductorsubstrate.

[0084] For the sake of clarity, FIG. 4 depicts only the metal layershatched, although the remaining areas or zones are also depicted incross-section.

[0085] In the p-conductive areas 5, there is a p-charge excess in a zoneI, a “neutral” charge in the zone II, and an n-charge excess in zoneIII. This means that in the area 5 which forms a “p-column” in the zoneI, the charge of the p-column dominates the charge of the surroundingn-conductive area 5, further that in the zone II, the charge of thep-column precisely compensates the charge of the surrounding n-area 5,and that in the zone III, the charge of the p-column does not yetdominate the charge of the surrounding n-area 5. It is also essentialthat the charge of the p-areas 5 is variable, whereas the charge of then-areas 4 is in each case constant. However, it is possible here, as inthe preceding exemplary embodiments, that the charge of the p-conductiveareas 5 is constant and the charge of the n-conductive areas is varied.It is likewise possible to design the charge variable in both areas 4and 5.

[0086]FIG. 5 depicts in a cross-section C-D the course of the degree ofcompensation K over the depth t of the n-channel MOS transistor: As isdiscernible from FIG. 5, the degree of compensation K risesmonotonically with a constant gradient or in steps from the point C topoint D.

[0087] It is discernible from FIG. 6 that the electrical field E has asubstantially constant curvature over the area 5 between the points Cand D.

[0088]FIG. 7 depicts compensation parabolas for a constant and avariable doping of the p-conductive areas 5 in the exemplary embodimentof FIG. 4. The degree of compensation K is plotted in percentages on theabscissa, whereas the ordinate indicates the breakdown voltage U involts. One curve 11 depicts the breakdown voltage U for a variabledoping, whereas a curve 12 depicts the breakdown voltage for a constantdoping. It is clear that the variable doping brings a considerable dropin the breakdown voltage from approximately 750 V to approximately 660V. However, in exchange, a larger range of the degree of compensationcan be used.

[0089]FIG. 8 depicts finally a cell design in a cross-section with adrain D, a source S, and a gate G, the n⁺-conductive semiconductorsubstrate 1, an n-conductive semiconductor region 13, the n-conductivelayer 3, and n-conductive regions 4 as well as p-conductive regions 5for the p-conductive region 5 under the source electrode S. In FIG. 8the degrees of compensation, for example, between +30% and −20% arereported, whereby a degree of compensation “0” indicates truecompensation between n-doping and p-doping. Here, the doping thus varieswithin the “p-column” by a factor 3 whereas the doping in the“n-columns” is constant.

[0090]FIGS. 9a through 9 c depict, in principle, as in FIGS. 3a through3 d, how the semiconductor device according to the invention can bedesigned with different structures which extend into the edge region. Ascan be discerned in FIG. 9a through c, FIG. 10a through c and in FIG.11, in the semiconductor edge region, a large number of floating zones5′, are formed from the second conductivity type and are separated fromintermediate zones 4′ of the first conductivity type. The width of theintermediate zones 4′ and the widths of the floating zones 5′ aresmaller than the widths of the regions 4, 5 inside the cell field. Thefloating zones 5′ and the intermediate zones 4′ are dimensioned suchthat their charge carriers are completely cleared with the applicationof blocking voltage. The zones 5′, which are designed lightly p-doped inthe present exemplary embodiment, are “floating”, i.e., they have anundefined potential. The floating zones 5′ are positioned at a distancefrom each other, whereby the region between the floating zones 5′defines an intermediate zone 4′. This intermediate zone 4′ typically hasthe same doping concentration as the doping in the zones 4 within thecell field.

[0091]FIG. 9a, b, and c depict different variations of the widths of thefloating zones compared to the basic widths in the cell field. FIG. 10a,b, and c depict the same thing with the strip edge structure layout andFIG. 11 with a hexagonal edge structure layout.

[0092]FIG. 12 and FIG. 13 depict the n-channel MOS transistor known fromFIG. 4, which has been expanded by an intrinsically compensated edgetermination. The transistor is built in known fashion with ann⁺-conductive silicon semiconductor substrate 1, a drain electrode 2, afirst n-conducting layer 13, a second layer with n-conducting areas 4and p-conductive areas 5, p-conductive zones 6, n-conductive zones 7,gate electrodes 8 made, for example, from polycrystalline silicon ormetal, which are embedded in an insulation layer 9 made, for example,from silicon dioxide, and a source metalization 10 made, for example, ofaluminum. In the present figures in each case two p-conductive areas 5and n-conductive areas 4 are depicted on the left side. Toward theright, additional p-conductive areas 5′ and n-conductive areas 4′ extendalternatingly. The p-conductive areas 5′ have, compared to thep-conductive areas 5, roughly half the width; however, they extendroughly as far into the n-conductive region 13 in the direction of thesubstrate 1. The regions 5′, 4′ lying adjacent the regions 4, 5 areconnected to a p-conductive zone 6′, which connects via a contact holewith the source metalization 10. The p-conductive zone 6′ forms a p-ringknown from the prior art. The p-conductive zones 6′ has, in contrast tothe cell field, no n-conductive zone, to prevent parasitic transistors.The n- and p-conductive areas 4′, 5′ extend far beyond the p-conductivezone 6′ in the direction of the edge of the device. On the outermostedge, there is a so-called channel stopper configuration, which consistsof a gate electrode 8′, which is electrically connected with ann-conductive zone 7′, which for its part is accommodated in ap-conductive zone 6′ in the n-conductive region 13.

[0093] The so-called space charge region stopper depicted in FIG. 13constitutes an alternative to the channel stopper configuration depictedin FIG. 12. This space charge region stopper consists only of a wellconductive n⁺-conductive zone, which is placed in the n-conductiveregion.

[0094] Common to both exemplary embodiments is the fact that the contactholes of the p-conductive zone 6′ are substantially larger compared tothe contact holes in the n- or p-conductive zones 7, 6. The result ofthis is that the gate electrode 8′, which lies above the areas 4′, 5′ isdesigned substantially smaller compared to the gate electrodes 8 of thecell field. The grid, in which the areas 4′, 5′ are arranged, is roughlyhalf as large as the areas 4, 5 of the cell field.

1. Semiconductor component having a semiconductor body comprising ablocking pn junction, a source zone of a first conductivity typeconnected to a first electrode and bordering on a zone forming theblocking pn junction of a second conductivity type complementary to thefirst conductivity type, and a drain zone of the first conductivity typeconnected to a second electrode, the side of the zone of the secondconductivity type facing the drain zone forming a first surface and, inthe region between the first surface and a second surface locatedbetween the first surface and the drain zone, regions of the first andsecond conductivity type nested in one another, wherein the regions ofthe first and second conductivity type are variably so doped that nearthe first surface doping atoms of the second conductivity typepredominate, and near the second surface doping atoms of the firstconductivity type predominate and further comprising a plurality offloating zones of the first and second conductivity type. 2.Semiconductor device according to claim 1, wherein the floating zonesform in the edge region of the semiconductor device a high-voltageresistant basic structure, and the floating zones are separated byintermediate zones of the first conductivity type, whereby the sum ofthe widths of one of the floating zone and one of the intermediate zoneis smaller than the sum of the widths of one of the area of the firstconductivity type and one of the areas of the second conductivity typeand the charge carriers of the floating zones and the intermediate zonesare completely depleted with the application of blocking voltage. 3.Semiconductor device according to claim 2, wherein at least one spacecharge region stopper is provided on the outermost edge of the edgetermination of the semiconductor device.
 4. Semiconductor deviceaccording to claim 3, wherein the space charge region stopper has aheavily doped zone of the first conductivity type arranged at or nearthe first surface and the second surface.
 5. Semiconductor deviceaccording to claim 4, wherein the space charge region stopper has adamage implanted area.
 6. Semiconductor device according to claim 5,wherein the space charge zone stopper has a metal or a polysiliconcontaining electrode which is connected to the semiconductor body. 7.Semiconductor device according to claims 1, wherein the areas of thefirst and second conductivity types are arranged laterally in thesemiconductor body.